1. Field of the Invention
The present invention relates to a disk testing apparatus, a disk testing method, a computer product, and a disk apparatus, and more particularly, to a disk testing apparatus, a disk testing method, a computer product for conducting a test on a disk apparatus while setting a predetermined condition of a recording density, and a disk apparatus tested by the above apparatus and method.
2. Description of the Related Art
Conventionally, a various kinds of tests are conducted on a magnetic disk apparatus before shipment. Technologies for such tests are disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2004-071061 and PCT Application Laid-Open Publication No. H11-514480. Generally, a head test is conducted on each head for the magnetic disk to rank the head according to specifications (a format condition such as a linear recording density and a track density) of a disk apparatus. A head ranked high is installed in a disk apparatus for which a format condition with high density is set. A head ranked low is installed in a disk apparatus for which a format condition with low density is set. Then, based on each of the format conditions set for the disk apparatus, test relating to readout of data, such as an error rate test and a side erase test, is conducted on the disk apparatus.
In the error rate test, the readout of data stored in a disk of the disk apparatus is tested for a plurality of times to determine an error rate, which is a probability of error in the readout. In the side erase test, the error rate when writing is conducted into a part adjacent to a part at which the data to be read is stored in the disk is determined by testing the readout of the data before and after the writing. Alternatively, another detection function that is included in a read channel (RDC) such as a Viterbi metric margin (VMM), which is a rate of erroneously selecting a value other than an optimal value determined in a Viterbi method, expressed numerically), may be used instead of the error rate.
Testing environment is different for the head and for the disk apparatus. For example, while the head test is conducted at room temperature, the test for the disk apparatus is conducted in a wide range of temperature from low to high. Moreover, while assembling the disk apparatus with the head and the disk, the head may be damaged, resulting change in a quality (rank) of the head. If the quality of the head changes, the head is often determined faulty in the test due to unsuccessful results in the error rate test and the side erase test, even though the disk apparatus is assembled depending on the rank initially determined for the head. When the head is determined faulty in the disk apparatus, the head is removed from the disk apparatus and re-assembled for a disk apparatus that is suitable for the rank of the head determined faulty. Then, a same process of the error rate test and the side erase test is repeated under a same format condition as the test conducted previously.
However, in the above conventional technologies, the head may be unnecessarily discarded. Moreover, an extra time and labor is spent on the test before shipment.
Specifically, in the above conventional technologies, the head determined faulty is removed from the disk apparatus to be discarded although even such head may pass the error rate test and the side erase test, if the head is used in a disk apparatus for which a format condition with a low density is set. In other words, the head is discarded unnecessarily, and this increases manufacturing cost of the disk apparatus.
Furthermore, in the above conventional technologies, if results of the error rate test and the side erase test are unsuccessful, the test is repeated on the disk apparatus after re-assembling the disk apparatus with a replaced head. Therefore, extra time and labor is spent on the test before shipment, hindering mass production of the disk apparatus.